强磁场下高临界电流密度Nb3Sn超导股线的应变特性研究

Nb3Sn superconductor is a typical A15-type compound, which has higher critical temperature and higher upper critical magnetic field, and is one of the most ideal material for the superconducting manget in the field more than 10 T. The critical current density of A15 compound is very sensitive to strain, due to the change of lattice parameter and the affecting to transport properties of superconducting filaments by the mechanical strain or stress. The thermal strain and the electro-magnetic strain produced during the machining and the operation of the large scale CICC superconducting magnet are unavoidable, and will inevitably infulence the critical current performance of the Nb3Sn strand, and even result in irreversible performance degradation. So there is a need to do in-depth study on the strain performance of Nb3Sn strand and its internal mechanism of critical current. This project will study the influences to the critical current performance of the Nb3Sn strands by axial strain and transverse strain from experiments; study the influences to the Nb3Sn compound with small and uniform grains by the heat treatment conditions; construct a mathematical model to analyse the influences rule of Nb3Sn critical current by the strain, and to promote people to understand the strain performance internal mechanism of the Nb3Sn strands, and this project will also provide a scientific basis for the design and stable operation of a 40 T hybrid magnet superconducting outsert.

Nb3Sn超导体是典型的A15型化合物，具有较高的临界温度和上临界磁场，是制作10T以上超导磁体最理想的高场超导材料之一。但由于机械拉伸或压缩会改变A15型化合物的晶格参数，影响超导细丝的输运性能，因此A15型化合物的临界电流密度对应变非常敏感。大型管内电缆（CICC型）超导磁体在加工和运行过程中产生的热应变和电磁应变是不可避免的，必然会对Nb3Sn股线的临界电流性能造成影响，甚至导致不可逆的性能退化，因而有必要针对Nb3Sn股线临界电流的应变特性以及内在机理做深入研究。本项目将实验研究轴向应变和横向应变对Nb3Sn股线临界电流性能的影响；研究热处理条件对获得晶粒细小、均匀的Nb3Sn化合物的影响；建立数学模型，分析应变对Nb3Sn临界电流的影响规律，增进人们对于Nb3Sn股线应变特性内在机理的理解，同时为40T混合磁体外超导磁体的设计和稳定运行提供科学的依据。

Nb3Sn 超导体是典型的A15型化合物，其临界电流密度对应变非常敏感。大型管内电缆（CICC 型）超导磁体在加工和运行过程中产生的热应变和电磁应变是不可避免的，必然会对Nb3Sn股线的临界电流性能造成影响，甚至导致不可逆的性能退化，因而有必要针对Nb3Sn股线临界电流的应变特性以及内在机理做深入研究。在本项目的支持下，我们研制了一套Nb3Sn超导股线低温性能测试装置，该装置能够研究温度、磁场、应变等参数的变化对Nb3Sn超导股线临界电流性能的影响。同时，通过模拟大型超导磁体的热处理条件，我们研究了故障态条件对Nb3Sn临界电流性能、RRR值、磁滞损耗等性能的影响；进而，以Nb3Sn股线的应变特性的研究成果为基础，我们针对CICC型超导导体、超导接头以及超导磁体的性能进行了详细的模拟分析，为45T混合磁体的稳定运行提供了必要的保障。